Windows Vista is adding new wrinkles to WAN optimization.

For one, Microsoft’s Vista client operating system incorporates a number of features aimed at improving the performance of applications over the WAN, including a rewritten TCP/IP stack and a new Common Internet File System (CIFS) implementation.

Microsoft also worked security enhancements into Vista, including server and domain isolation. This security feature lets administrators create virtual networks of Windows computers that adhere to policies -- set in Microsoft’s Active Directory -- which determine if in-bound connections should be accepted.

I wrote a story published this week in Network World that details the network impact of some of these Vista features. Analysts Joe Skorupa of Gartner and Eric Siegel of Burton Group weighed in with their opinions about how the WAN optimization market might change as a result.

When I was researching the story, I had a chance to chat with executives from a few WAN optimization vendors to get their insight on the network performance impact of Vista. Here are some of the issues they highlighted:

* Consistency is required. Some of the key new features built into Vista won’t be of any benefit to enterprises unless both ends of a connection can support these new features, says Bobby Guhasarkar, senior manager of product marketing at Juniper Networks. For example, the congestion control algorithms in the new TCP/IP stack and the new version of the Server Message Block (SMB) protocol used in CIFS (which lets multiple data blocks be sent over the WAN simultaneously) each require Vista or Longhorn Server to be running on both ends of a WAN link to be effective. “Any time you make something new on one side of a two-way conversation, the other side also has to understand all these new things,” Guhasarkar says.

* Expect some interference. Server and domain isolation could require a number of companies to adapt their WAN optimization techniques, says Gareth Taube, vice president of marketing at WAN acceleration vendor Certeon. With server and domain isolation, “every packet that’s transmitted by a Vista client has got a little header which authenticates the data in that packet,” Taube says. “What the operating system is doing -- and for good reason -- is asking ‘Do you want to send this data? Is this allowed?’”

Ann Bednarz is associate news editor at Network World.